Scientists have known for some time that tree rings record the history of avalanches. Now a new method allows them to study the rings without killing the tree.
The impact of an avalanche is clear on the outside of the tree. It breaks off branches and scrapes bark. But it also affects inside the tree. The growth rings become slightly irregular and warped.
Often scientists have studied regions where avalanches are common, such as Alaska and the Rocky Mountains. Tree ring records of avalanches in the Eaglecrest ski area of Alaska, for example, date back to the 1800s. In the Rockies, tree rings show that widespread avalanches occur about every five years.
Until recently, researchers had to cut down the tree to obtain a full cross-section of its trunk. But a new study in Bulgaria used a different method. Rather than chop down the tree, the team used an increment borer to extract thick wood cores from the trunks of hundreds of pine trees. The samples were then dried, mounted in holders, and sanded so the rings were visible.
“It’s a very long process,” admitted co-author Nickolay Tsvetanov.
Bansko, Bulgaria. Photo: Shutterstock
Researchers targeted the Bansko Ski resort in Bulgaria’s Pirin Mountains. Here, skiers and snowboarders are venturing off-piste in ever greater numbers, so understanding avalanche history is increasingly important.
The results showed that avalanches have occurred in the area since at least the 1600s, with 20 large-scale avalanches since the 1800s. Though one of these matches an avalanche record from February 12, 1963, the other mega-slides were completely unknown.
“We don’t have written histories of these events. We can only rely on tree rings,” commented co-author Momchil Panayotov, a Bulgarian dendrochronologist.
Through the tree rings, the team could estimate how large the various slides were. This meant they could date the avalanches and see how climate affected their occurrence and size. They hope the results will help with avalanche safety around the popular resort and beyond.
